The Justice Department’s Office of Professional Responsibility (OPR) has opened an investigation into a generous plea bargain awarded in 2007 by a top Florida prosecutor — who now serves as President Trump’s secretary of labor — to a wealthy, Clinton-connected financier and sex offender accused of abusing underage sex slaves.

But watchdog groups say the DOJ’s independent inspector general, Michael Horowitz, should be spearheading the probe, rather than OPR — which is run by internal agency lawyers.

Earlier this week, Horowitz urged lawmakers to swiftly pass legislation that would enable the IG’s office to take control of probes into possible prosecutorial misconduct.

Alexander Acosta negotiated what critics are calling a sweetheart, potentially corrupt plea deal with Jeffrey Epstein when he was the U.S. attorney for the Southern District of Florida. The arrangement required Epstein to pay restitution to dozens of victims, but offered a variety of unusual concessions as part of a non-prosecution agreement.

Epstein allegedly operated his sex ring at his mansion in Palm Beach, Florida, a residence in New York City, and his private island estate on the 72-acre Virgin Islands home dubbed by some “Orgy Island.” He ultimately served 13 months in jail and registered as a sex offender after pleading guilty to two felony prostitution charges, with only one involving a girl that prosecutors called a prostitute — even though she was only 14 years old.

“Jeffrey Epstein is a child rapist and there’s not a single mom or dad in America who shouldn’t be horrified by the fact that he received a pathetically soft sentence,” Nebraska Republican Sen. Ben Sasse, who pushed for the probe, said in a statement Wednesday. “The victims of Epstein’s child sex trafficking ring deserve this investigation – and so do the American people and the members of law enforcement who work to put these kinds of monsters behind bars. Parents should be grateful for the men and women at the DOJ who are committed to transparency and accountability and for the soon-to-be Attorney General who is committed to pursuing justice.”

The plea deal awarded to Epstein guaranteed immunity to “any potential co-conspirators” of Epstein — a provision that signaled prosecutors’ willingness to effectively end the federal investigation into potential crimes committed by Epstein associates. And the deal was kept under seal, meaning potential victims would have difficulty finding out about it and objecting to its terms. Some reportedly only found out about the deal from hearing about it on television.

The Miami Herald identified several other apparent signs that prosecutors were working closely with Epstein’s team. In one instance, a top federal prosecutor on the case, A. Marie Villafaña, wrote to Epstein’s lawyer, Jay Lefkowitz, that she would help his client avoid unwanted press attention.

Labor Secretary Alex Acosta is formerly the dean of the Florida International University College of Law. During his confirmation hearings, he was grilled about the Epstein plea deal.(Reuters/Aaron P. Bernstein)

In a letter to Sasse, the Justice Department said it would specifically review whether any federal prosecutors had committed “professional misconduct” and promised a “thorough” investigation.

“[The Department of Justice Office of Professional Responsibility] (OPR) has now opened an investigation into allegations that Department attorneys may have committed professional misconduct in the manner in which the Epstein criminal matter was resolved,” the DOJ said in its letter to Sasse. “OPR will thoroughly investigate the allegations of misconduct that have been raised and, consistent with its practice, will share its results with you at the conclusion of its investigation as appropriate.”

Flight logs show Clinton flew on Epstein’s private jet dozens of times

Last year, Iowa Republican Sen. Chuck Grassley introduced legislation that would permit the independent IG to review allegations of attorney misconduct instead of OPR, and the House of Representatives has overwhelmingly approved the measure by voice vote. The Inspector General Access Act is now pending before the senate.

“Misconduct by DOJ attorneys is a serious matter and should be investigated by an independent Inspector General, not by other Department attorneys, so there is no real or perceived conflict of interest,” Grassley said in a statement last June. “This bill ensures that the Justice Department’s inspector general is able to access and independently evaluate allegations of misconduct by Justice Department attorneys.”

Critics pointed in particular to remarks by Acosta in his confirmation hearing when he was challenged by senators about the deal.

“Secretary Acosta doesn’t just believe it was appropriate to let a wealthy, connected man involved in rampant child sex abuse walk away with a slap on the wrist, he actually considers it a ‘point of pride’ – even worse, a ‘good thing,’” Jeremy Funk, a spokesman for the watchdog group Allied Progress, said in a statement to Fox News. “While it’s certainly a good thing someone with such a weak dedication to justice is no longer a U.S. Attorney, Acosta still must answer for his gross misconduct during that time. All eyes are on the Senate to stop stalling, stop blindly protecting the Trump administration and give the Inspector General the authority he has asked for. The ball is currently in Senate Judiciary Chairman Graham’s court. Senators will continue to hear from constituents if Graham drops it.”

Allied Progress announced Wednesday it is embarking on a marketing blitz this week, targeted at lawmakers, to push for the swift passage of the Inspector General Access Act.

This July 30, 2008 photo shows Jeffrey Epstein in custody in West Palm Beach, Fla. Epstein was suspected nearly a decade ago of paying for sex with underage girls. The FBI abruptly dropped its investigation a few years ago, and Epstein pleaded guilty to a single state charge of soliciting prostitution. He served 13 months in jail. Now, two women who say they were sexually abused as girls by Epstein are hoping a trove of new documents will get the case reopened. (AP Photo/Palm Beach Post, Uma Sanghvi)(The Associated Press)

Funk added: “It remains troubling that someone like Alex Acosta with a clear lack of judgement is serving as the nation’s Labor Secretary and is in a position make more decisions that benefit the powerful at the expense of the powerless, but on a much larger scale.”

“That is not accurate,” Acosta, who at the time was dean of Florida International University’s law school, responded. ““It was a broadly-held decision. … The grand jury recommended a single count of solicitation not involving minors. That would have resulted in zero jail time, zero registration as a sexual offender and zero restitution for the victims in this case.”

Instead, Acosta said, he pushed to escalate Epstein’s case to the federal level, even as he recognized that proving all of the allegations against him would be difficult.

“It was highly unusual where a U.S. attorney becomes involved in a matter that has already gone to the grand jury at the state level,” Acosta told senators. “We decided that Mr. Epstein should plead guilty to two years, register as a sexual offender, and concede liability so the victims should get restitution in this matter.”

Asked about keeping the deal confidential, Acosta suggested that he was following common practice.

“Something that I think has changed over time is trust of government,” he said. “There was a time when keeping something confidential was less of an issue, but the public expectation today is that things be very public.”

The Trump administration has suggested the issue is overblown. Epstein and Trump were friends in the past, and one of Epstein’s accusers told the Herald she was 16 years old and working at Mar-a-Lago as a locker room attendant when an Epstein associate approached her.

“This matter has been publicly addressed previously, including during confirmation hearings,” a Labor Department spokesperson told Fox News last year. “The U.S. Attorney’s Office for the Southern District of Florida has defended the actions in this case across three administrations.”

The U.S. Attorney’s Office in Florida declined to comment when reached by Fox News.

In December, the numerous young women who said they were sexually abused by Epstein reached a settlement in their civil case, meaning they were no longer appear set to testify about their bombshell allegations.

The case has potentially broad ramifications, given Epstein’s high-profile connections. Court documents obtained by Fox News in 2016 showed former President Bill Clinton took at least 26 trips flying aboard Epstein’s private jet, known as the “Lolita Express,” and apparently ditched his Secret Service detail on some of the excursions.

Authorities who seized trash outside Epstein’s home at the time found an invoice for the purchase of the book “SlaveCraft: Roadmaps for Erotic Servitude — Principles, Skills and Tools,” as well as the instructional “Training with Miss Abernathy: A Workbook for Erotic Slaves and Their Owners.”